1function numberWithCommas(x) {
2  return x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ',');
3}

1var n = 34523453.345
2n.toLocaleString()
3"34,523,453.345"
4

1// Convert a number to a string with commas
2function numberWithCommas(x) {
3    return x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
4}
5
6// Convert a number to a string with commas taking into account decimal point
7function numberWithCommasDecimal(x) {
8    return x.toString().replace(/\B(?<!\.\d*)(?=(\d{3})+(?!\d))/g, ",");
9}

1x.toString().toLocaleString(); // x must be a number